A. Field of the Invention
The field of the present invention relates generally to apparatuses and methods for improving and enhancing respiratory ventilation of live subjects. More particularly, the present invention relates to such apparatuses and methods which are capable of generating and transmitting vibrations to the lungs of a subject so as to augment diffusion of gases across the alveolar membrane, increase effective contact surface, prevent focal alveolar collapse, enhance effective expectoration and improve blood perfusion of the lungs. Even more particularly, the present invention relates to such apparatuses and methods which can be utilized independently or in combination and cooperatively with any type of ventilator machine.
B. Background
As is well known, the human body normally obtains the oxygen it needs to sustain life through a process of respiration or breathing that causes air to be inhaled and carbon dioxide to be exhaled through the mouth and nose. In the human body, the lungs are the organs that function to transmit oxygen from the inhaled air to the blood supply. The lungs have a plurality of successively branching bronchioles, essentially in the shape of an upside down tree, that are in gas exchange communication with the alveolar network of blood capillaries. The air obtained from respiration is transmitted from the alveoli to the capillaries. Due to injury, disease, prematurity, surgery or other circumstances, it can be necessary to provide respiratory assistance to a living subject.
In the field of medicine, conventional mechanical ventilators (CMVs) are utilized for ventilating the lungs of a patient who is either not able to breath on his or her own or who has respiratory failure of any cause. Typically, CMVs are configured to operate at tidal volumes, which is the amount of gas given with each breath, and frequency, which is the rate of the tidal volumes given in a minute, that approximate normal breathing patterns. For instance, a typical tidal volume for these machines is approximately 7 mL of gas for each Kg of body weight (7 ml/Kg), which is close to the 500 mL breathing volume that is normally expected of a 70 Kg healthy human being, and a typical rate can be 12-18 times per minute for an adult and 35-45 times per minute for a new-born. As a result, CMVs usually have a limit of up to 60 breaths per minute. The CMV provides a mixture of oxygen and air, or other breathable gases, to the patient at the necessary breath rates. Most CMVs can be fine tuned to the needs of the patient based on the fraction of inspired oxygen (FIO2) level, inspiration and expiration timing and volume/pressure limit settings. The typical CMV does not use negative pressure during exhalation, depending instead on the tendency of the lungs to deflate spontaneously. Often, some residual pressure is maintained during expiration, which is called positive end expiratory pressure (PEEP), in order to prevent collapse of the alveoli. A schematic representation of the way in which CMVs give breath to a subject is shown in FIG. 1.
High frequency ventilators (HFV) were developed to provide the benefits of using higher breath rates in certain patients, particularly small neonates. These HFV machines use much higher respiratory rates combined with significantly lower tidal volumes (i.e., respiratory rates of 150-550 per minute and tidal volumes of 3-5 mL). Unfortunately, HFV machines were found to have the disadvantage of over-inflating the patient's lungs. Due to this problem and the emergence of active (negative pressure) expiration phase concepts, high frequency oscillatory ventilators (HFOV) were developed. A scheme of the way in which HFOV machines ventilate a patient's lungs is shown in FIG. 2. Other types of HFVs include combined conventional and high frequency ventilators, and the high frequency jet ventilator (HFJV), which uses multiple conduit endotracheal tubes and has the advantage of eliminating the dead-space of the proximal airways. Some of these more sophisticated machines are able to give a combination of high frequency small tidal volumes along with regular low rate breaths given by CMVs. A scheme of the way combination machines ventilate a patient's lungs is roughly shown in FIG. 3. Other types of HFVs are the high frequency fan ventilator (HFFV), high frequency flow interruption and high frequency chest wall oscillation.
Although not directly related to artificial ventilators, the bubble continuous positive airway pressure (Bubble CPAP) system is a relatively simple system that is suited for more stable patients. In this system, the inhaled gas passes through a sealed container half filled with water or like fluid prior to entering the subject's respiratory systems. In operation, a mixture of breathable gas enters the container through a first tube that has its tip submerged in the fluid and exits the container through a second tube that is sealed and secured to the lid of the container and configured to direct the breathable gas towards the patient. When the gas is pushed into the first tube with enough pressure, typically a few centimeters of water, bubbles result. The vibrations and/or subtle changes in the pressure of the inhaled gas created by the bubbles were found to improve the patient's oxygenation. The Bubble CPAP system, which is used in many hospitals nowadays with excellent results, illustrates the physiologic benefits of even a mild pressure oscillations on respiration. Bubble CPAP, however, cannot be used for patients who are unable to generate sufficient intrathoracic negative pressure to inhale a sufficient amount of breathable gas, despite the fact that positive pressure is given to the airways by the machine. The benefits of biologically variable (noisy) and stochastic ventilators for the treatment of respiratory distress syndrome (RDS) and atelectasis, as well as certain other respiratory conditions, is also well known and experienced.
The exact mechanism by which the HFV, stochastic noisy ventilator or bubble CPAP can improve a subject's oxygenation is not fully understood by those skilled in the art. It has been postulated that the vibrations from these machines are transmitted to the alveoli and quickly displace the gas immediately in contact with the alveolar membrane. These vibrations, or pulsations, also seem to be able to inflate the collapsed alveoli at lower pressures compared with CMV. The same strategy of generating intrathoracic vibrations is used in nature to augment respiration and oxygenation. Examples of such natural mechanisms are the crying of the newborn babies right after birth, grunting during sickness, groaning when in danger, growling in extreme anger and moaning during sexual intercourse.
One of the reasons why HFV works better than CMV might be the fact that minute volume (which is the amount of gas given to the lungs in one minute) is a more important parameter in ventilation of lungs than tidal volume. Although HFVs have tidal volumes equal or even less than the dead-space and, therefore, significantly less than the tidal volumes in CMVs, because breath rate in the HFV machine is significantly higher than CMV machine, the minute ventilation is remarkably higher in the HFV. As an example, in a 2 Kg baby on CMV with IMV rate of 40 per minute, minute volume would add up to approximately 560 mL (2×7×40=560). The same baby on a HFV will roughly receive 800-1200 mL of minute volume (assumming tidal volume of 2-3 mL and oscillation frequency of 400/min).
One of the major side effects of artificial ventilation of any kind is the development of chronic lung disease and life long morbidities. These side effects usually happen at higher pressures, higher FIO2, and prolonged ventilation. Therefore, it is highly desirable to use as low pressure and FIO2 setting for the shortest period possible. Because vibration of the alveolar membrane is the mainstay of improved respiration, and considering the fact that vibratory energy is known to dissipate along narrow tubes, in order to effectively improve respiration without being harsh on proximal airways it is necessary to use higher frequency vibrations. With higher frequency vibrations, it is possible to use lower pressures and milder oscillations to keep the alveoli open and rumbling, which is much less likely to result in damage to the lungs. Although the prior art discloses a variety of apparatuses and methods for enhancing ventilation of a human subject and despite the known or apparently known benefits of delivering vibratory energy to the lungs of a subject to improve oxygenation and decarbonization in health and sickness, no apparatus or method is known to beneficially and directly provide such vibratory effect to enhance ventilation, particularly the ability to effectively deliver these vibrations to terminal bronchioles and alveoli. Tests by the inventor indicate that the lower frequency vibrations generated by HFVs are not sufficient to deliver vibratory energy to terminal bronchioles and alveoli. It is postulated that frequencies of approximately 200-4000 Hz are necessary, depending on the size of the subject and/or his/her medical condition, to deliver the desired vibratory energy to the terminal bronchioles and alveoli. What is needed, therefore, is an apparatus and method of delivering vibrations to the lungs of a living subject without harming the airways and/or alveoli.